1. Field of the Invention
The present invention relates to a power tool that performs a screw-tightening operation or a drilling operation and more particularly, to a technique to mount a tool bit to the power tool with a simple construction.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 2000-218412 discloses a driver bit mounting device for an impact driver. According to the known device, the tool bit is mounted simply by inserting the driver bit into the bit mounting hole of the tool holder. In the known device, an, elongate hole radially extends through the tool holder having a bit mounting bole and has a predetermined length in the axial direction. A steel ball is disposed in the elongate hole and can move in the both axial and radial directions of the tool holder. The steel ball is biased by a ring spring such that part of the steel ball protrudes into the bit mounting hole. When the driver bit inserted into the bit mounting hole, the steel ball is pushed by the lip end portion of the driver bit and once moves in the axial direction while expanding the ring spring in diameter. Thereafter, the steel ball further moves outward in the radial direction, so that the driver bit is allowed to be inserted When the driver bit is inserted until the groove (notch) of the driver bit faces the steel ball, the steel ball moves inward in the radial direction by the restoring force of the ring spring and then moves in the axial direction into engagement with the groove. As a result, the driver bit is prevented from moving into the direction of removal and locked in the inserted position.
In the known art, after insertion of the driver bit, the steel ball which is in engagement with the groove of the driver bit is prevented from moving outward in the radial direction by a movement preventing portion of a cylindrical opting sleeve fitted on the tool holder. Thus, the steel ball is held engaged with the groove of the driver bit With such construction, the ring spring is necessarily indispensable for moving the steel ball in the axial direction into a position in which the steel ball faces the movement preventing portion of the operating sleeve. Thus, the number of parts is increased and the structure is complicated.